The field of rapid prototyping involves the production of prototype articles and small quantities of functional parts, as well as structural ceramics and ceramic shell molds for metal casting, directly from computer-generated design data.
Two well-known methods for rapid prototyping include a selective laser sintering process and a liquid binder three-dimensional printing process. These techniques are similar to the extent that they both use layering techniques to build three-dimensional articles. Both methods form successive thin cross-sections of the desired article. The individual cross-sections are formed by bonding together adjacent grains of a granular material on a generally planar surface of a bed of the granular material. Each layer is bonded to a previously formed layer to form the desired three-dimensional article at the same time as the grains of each layer are bonded together. The laser-sintering and liquid binder techniques are advantageous, because they create parts directly from computer-generated design data and can produce parts having complex geometries. Moreover, three-dimensional printing can be quicker and less expensive than machining of prototype parts or production of cast or molded parts by conventional “hard” or “soft” tooling techniques, that can take from a few weeks to several months, depending on the complexity of the item.
Three-dimensional printing has been used to make ceramic molds for investment casting, to produce fully functional cast metal parts. Additional uses are contemplated for three-dimensional printing. For example, three-dimensional printing may be useful in design-related fields for visualization, demonstration, and mechanical prototyping. It may also be useful for making patterns for molding processes. Three-dimensional printing techniques may be further useful, for example, in the fields of medicine and dentistry, where expected outcomes may be modeled prior to performing procedures. Other businesses that may benefit from rapid prototyping technology include architectural firms, as well as others in which visualization of a design is useful.
A selective laser sintering process is described in U.S. Pat. No. 4,863,568, incorporated herein by reference in its entirety. The selective laser sintering process has been commercialized by DTM Corporation. The selective laser sintering process involves spreading a thin layer of powder onto a flat surface. The powder is spread using a tool developed for use with the selective laser sintering process, known in the art as a counter-rolling mechanism or counter-roller. Using the counter-roller allows thin layers of material to be spread relatively evenly, without disturbing previous layers. After the layer of powder is spread onto the surface, a laser is used to direct laser energy onto the powder in a predetermined two-dimensional pattern. The laser sinters or fuses the powder together in the areas impinged upon by the laser beam energy. The powder may be plastic, metal, polymer, ceramic or a composite. Successive layers of powder are spread over previous layers using the counter-roller, followed by sintering or fusing with the laser. The process is essentially thermal, requiring delivery by the laser of a sufficient amount of energy to sinter the powder together, and to previous layers, to form the final article.
An early three-dimensional printing technique, described in U.S. Pat. No. 5,204,055, incorporated herein by reference in its entirety, describes the use of an ink-jet style printing head to deliver a liquid or colloidal binder material to sequentially applied layers of powdered material. The three-dimensional ink-jet printing technique or liquid binder method involves applying a layer of a powdered material to a surface using a counter-roller. After the powdered material is applied to the surface, the ink-jet printhead delivers a liquid binder in a predetermined pattern to the layer of powder. The binder infiltrates into gaps in the powder material and hardens to bond the powder material into a solidified layer. The hardened binder also bonds each layer to the previous layer. After the first cross-sectional portion is formed, the previous steps are repeated, building successive cross-sectional portions until the final article is formed. Optionally, an adhesive can be suspended in a carrier that evaporates, leaving the hardened adhesive behind. The powdered material may be ceramic, metal, plastic or a composite material, and may also include fibers. The liquid binder material may be organic or inorganic. Typical organic binder materials used are polymeric resins or ceramic precursors, such as polycarbosilazane. Inorganic binders are used where the binder is incorporated into the final articles; silica is typically used in such an application.
One advantage of using an ink-jet print head, rather than a laser, is that a plurality of spray nozzles used to deliver binder to the powder may be arranged side-by-side in a single print head. In selective laser sintering machines, only one laser is conventionally used to deliver energy to the powder. The combination of several spray nozzles increases the speed of liquid binder printing in comparison to laser-sintering, by allowing a larger area to be printed at one time. In addition, liquid binder printing equipment is much less expensive than the laser equipment, due to the high cost of the laser and the high cost of the related beam deflection optics and controls.
The powders, especially metallic powders, presently used in both selective laser sintering and liquid binder techniques present safety issues that may render them undesirable for use in an office environment. These safety issues may require special clothing and processing facilities to prevent, for example, skin contact or inhalation of toxic materials. In addition, more expense may be incurred through complying with regulations for the disposal of toxic materials. For these reasons, these techniques do not lend themselves to being used in typical office environments, such as architectural and design firms, or doctor's offices.
Another three-dimensional printing technique, described in U.S. Pat. Nos. 5,902,441 and 6,416,850, both references incorporated herein by reference in their entirety, utilizes a powder mixture containing a filler and an activatable adhesive in conjunction with an aqueous fluid that activates the adhesive to bind the filler. The fluid is applied by an ink-jet printhead. The filler and adhesive may each include non-toxic materials such as, for example, water-soluble polymers, carbohydrates, sugars, sugar alcohols, proteins, and some inorganic compounds.
There exists a need in the art for a materials system and method that enables the quick, reliable, safe, and inexpensive fabrication of appearance models and small batches of functional parts in an office environment. Such appearance models and parts need to have good-quality surfaces, to be accurately defined, and to be strong without being brittle. Furthermore, some kinds of models need specific mechanical properties such as flexibility for snap-fits or impact toughness.